1 files changed, 25 insertions, 3 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 29223daab7..118f412d4a 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -7673,18 +7673,40 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
         unsigned Size = MemOpLength->getZExtValue();
         unsigned Align = cast<ConstantInt>(CI.getOperand(4))->getZExtValue();
         PointerType *NewPtrTy = NULL;
+        unsigned numBits = Size << 3;
         // Destination pointer type is always i8 *
         // If Size is 8 then use Int64Ty
         // If Size is 4 then use Int32Ty
         // If Size is 2 then use Int16Ty
         // If Size is 1 then use Int8Ty
         if (Size && Size <=8 && !(Size&(Size-1)))
-          NewPtrTy = PointerType::get(IntegerType::get(Size<<3));
+          NewPtrTy = PointerType::get(IntegerType::get(numBits));
 
         if (NewPtrTy) {
-          Value *Src = InsertCastBefore(Instruction::BitCast, CI.getOperand(2), NewPtrTy, CI);
+          Value *L = NULL;
+          // If source is a null terminated constant c string then try to use immediate store.
+          if (Constant *C = dyn_cast<Constant>(CI.getOperand(2))) {
+            const std::string &Str = C->getStringValue();
+            if (!Str.empty()) {
+              APInt StrVal(numBits, 0);
+              unsigned len = Str.length();
+              APInt SingleChar(numBits, 0);
+              for (unsigned i = 0; i < len; i++) {
+                SingleChar = (uint64_t) Str[i];
+                StrVal = (StrVal << 8) | SingleChar;
+              }
+              // Append NULL at the end.
+              SingleChar = 0;
+              StrVal = (StrVal << 8) | SingleChar;
+              L = ConstantInt::get(StrVal);
+            }
+          }
+          // Otherwise load source from memory.
+          if (L == NULL) {
+            Value *Src = InsertCastBefore(Instruction::BitCast, CI.getOperand(2), NewPtrTy, CI);
+            L = new LoadInst(Src, "tmp", false, Align, &CI);
+          }
           Value *Dest = InsertCastBefore(Instruction::BitCast, CI.getOperand(1), NewPtrTy, CI);
-          Value *L = new LoadInst(Src, "tmp", false, Align, &CI);
           Value *NS = new StoreInst(L, Dest, false, Align, &CI);
           CI.replaceAllUsesWith(NS);
           Changed = true;